From: Will Deacon <email@example.com>
To: Stephen Smalley <firstname.lastname@example.org>
Cc: email@example.com, firstname.lastname@example.org
Subject: Re: [RFC PATCH 1/2] selinux: Don't call avc_compute_av() from RCU path walk
Date: Wed, 20 Nov 2019 13:12:30 +0000 [thread overview]
Message-ID: <20191120131229.GA21500@willie-the-truck> (raw)
Thanks for the quick reply.
On Tue, Nov 19, 2019 at 01:59:40PM -0500, Stephen Smalley wrote:
> On 11/19/19 1:40 PM, Will Deacon wrote:
> > 'avc_compute_av()' can block, so we carefully exit the RCU read-side
> > critical section before calling it in 'avc_has_perm_noaudit()'.
> > Unfortunately, if we're calling from the VFS layer on the RCU path walk
> > via 'selinux_inode_permission()' then we're still actually in an RCU
> > read-side critical section and must not block.
> avc_compute_av() should never block AFAIK. The blocking concern was with
> slow_avc_audit(), and even that appears dubious to me. That seems to be more
> about misuse of d_find_alias in dump_common_audit_data() than anything.
Apologies, I lost track of GFP_ATOMIC when I reading the code and didn't
think it was propagated down to all of the potential allocations and
string functions. Having looked at it again, I can't see where it blocks.
Might be worth a comment in avc_compute_av(), because the temporary
dropping of rcu_read_lock() looks really dodgy when we could be running
on the RCU path walk path anyway.
next prev parent reply other threads:[~2019-11-20 13:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 18:40 [RFC PATCH 0/2] Avoid blocking in selinux inode callbacks on RCU walk Will Deacon
2019-11-19 18:40 ` [RFC PATCH 1/2] selinux: Don't call avc_compute_av() from RCU path walk Will Deacon
2019-11-19 18:59 ` Stephen Smalley
2019-11-20 13:12 ` Will Deacon [this message]
2019-11-20 15:28 ` Stephen Smalley
2019-11-20 19:07 ` Paul E. McKenney
2019-11-20 19:13 ` Will Deacon
2019-11-19 18:40 ` [RFC PATCH 2/2] selinux: Propagate RCU walk status from 'security_inode_follow_link()' Will Deacon
2019-11-19 18:46 ` Stephen Smalley
2019-11-20 13:13 ` Will Deacon
2019-11-20 13:31 ` Stephen Smalley
2019-11-29 7:36 ` [selinux] 5149a783b9: WARNING:at_security/selinux/avc.c:#avc_has_perm_flags kernel test robot
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